This invention relates to full-wave, demand-controlled, pre-regulating power supply circuits in general, and in particular to such a circuit which includes a pair of gated rectifier means and a control means for insuring that alternate ones of said gated rectifier means will supply rectified current or voltage to the output of the circuit.
In general, power supply systems designed for use in point-of-sale terminals, such as electronic cash registers for example, typically used a traditional half or full-wave bridge rectifier circuit driving a storage/regulator type system. While this system has worked well and is still widely used, it has severe disadvantages in terms of cost, heat dissipation problems, size of components required, and efficiency as a result of load current variations.
Because of the demand characteristics of certain loads, it is possible that a particular load will draw current at a frequency which corresponds to the charging frequency of one of the silicon controlled rectifiers in a conventional full wave rectifier circuit. When this occurs, it is possible that the entire rectification load will fall upon one of the two silicon controlled rectifiers in the circuit, causing it to overheat or become damaged. The present invention obviates this problem to insuring that alternate ones of the gated rectifier means such as silicon controlled rectifiers, and the like, are used to supply the rectified current as needed. Also, because the load is positively distributed between the two gated rectifier means, a lower-rated transformer may be used with this invention, as excessive loading on one of the two secondary windings of the transformer is obviated.
Another feature of this invention is that when the load demand is reduced, or when the rectified voltage at the output of circuit is above a predetermined level, both gated rectifier means will be turned off, thereby minimizing heat dissipation within the circuit.
Some representative prior art power supply circuits are found in the following U.S. Pat. Nos.: 3,781,632; 3,939,394; 3,959,716; 3,969,665; 3,987,354; and 3,987,356.
None of these patents shows the use of a control circuitry for balancing the rectification load between two gated rectifier means in a full wave power supply circuit so as to permit the use of a smaller or lower rated power transformer and smaller heat sinks in the circuit, thereby lowering its cost.